It is known that glass can be treated to reduce glare (reflection) by making use of two different physical phenomena, diffusion and anti-reflection. Diffusion refers to the phenomenon by which reflections of light are scattered in various directions, so that the intensity of the reflections in the direction of a viewer is reduced, but the total hemispherical reflection remains the same. “Diffusion etching” treats a glass surface to increase the diffusion effect. Reducing glare by diffusion may be achieved by roughening the glass surface using physical or chemical means, e.g., by grinding, sand blasting, or acid etching.
Frosted glass is a typical light diffusion material which is usually made by acid etching of the glass surface. However, frosted glass cannot be used in applications where high clarity is required along with low glare. Examples of such applications are in picture frames; a protective surface for a cathode ray (picture) tube in television receivers; or as a screen for computer monitors. The above applications require a high level of clarity to prevent distortion of the images and colors displayed by a picture, such as a photograph, or to prevent detracting from the visual appreciation of the image. It is also desirable and important to reduce glare to prevent reflected light from interfering with observation of the picture or photograph contained therein. The reduction of glare is of particular importance in computer monitors where fatigue or stress may be induced by unwanted reflections. At the same time, image clarity must be maintained to minimize distortion. Distortion can cause eye strain if the image is viewed for long periods for time. Various attempts have been made to improve the light transmission qualities of frosted glass. However, the degree of clarity that has been achieved in such products has not been sufficient to enable them to be used in picture frames or in monitor screens.
Anti-reflection glass uses the principal of destructive interference. This results when incident light is reflected from an anti-reflection surface of a glass sheet. Trapping the light at particular wavelengths results is an actual reduction in the total light reflected. This includes the light that is directed toward the viewer. Although the total light reflected is reduced, the transmission (clarity) is increased. Such anti-reflection effects are usually achieved by applying one or more coatings to the sheet glass surface. Such coatings may be an inorganic metal oxide, which may be deposited by vacuum deposition, sputtering or sol gel deposition. However, anti-reflection processes are quite costly and therefore the treated glass is not economical for use in high-volume applications such as in picture frames or for replacing common glass. Consequently, low glare, high clarity sheet glass has not been generally available for use in these applications due to either poor clarity or high cost.
U.S. Pat. No. 5,120,605 to Zuel et al. discloses combining surface structures through both diffusion etching and anti-reflective etching to provide a low reflectance, high clarity glass at a low cost. However, such glass is difficult to clean using common household glass cleaners. Grease marks, which commonly occur on glass surfaces such as picture frames and cathode ray tubes, are especially difficult to remove without special high-strength glass cleaner. Such specialty high-strength glass cleaners are not normally available to the general public and are expensive.